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Combination of Heatwaves and Drought May Convert Carbon Sinks into Carbon Sources

Droughts and heatwaves are becoming more common place and more severe. They impact the carbon and water cycles in terrestrial ecosystems, which affect the carbon sequestration capability of terrestrial ecosystems. As these extreme climate events become more common, their effects, both separately and together, on the atmospheric carbon balance will be important for accurately projecting global warming’s progression. Yuan et al. (2016) examined the effects of a heatwave and drought in Southern China in the summer of 2013. They found that this drought and heatwave were the most severe experienced in the last 113 years. These events significantly altered the carbon cycle in the region, decreasing carbon uptake enough to convert the region from its historical role as a carbon sink to a carbon source of nearly the same size during July and August of 2013.

The authors found that the productivity of the vegetation in this area was significantly reduced by the drought and heatwave. Soil moisture was also reduced. These two trends were closely tied, leading the authors to suggest that decreased soil water content could be a major driver for lower vegetation production. Crop yields also fell during the drought by an average of 90.91 kilograms per hectare. Additionally, the data showed that vegetation had not recovered from the stress of heat and drought in September. This points to one noted limitation of this study; it only examines the immediate consequences of drought on the carbon uptake of terrestrial ecosystems. It suggests that longer term effects are likely to be significant as well and should be investigated.

In the larger context of climate change prediction, this study offers the insight that anticipated increased carbon sequestration due to longer growing seasons and warmer temperatures predicted in some regions may be cancelled out by more regular droughts that erode the ability of ecosystems to store carbon. This would contribute to a positive carbon-climate feedback loop and is a crucial consideration in making climate change predictions.